Method of and apparatus for making articles from powdered metal briquets



Dec. 13, 1960 J. B. BRENNAN 2,964,400

METHOD OF AND APPARATUS FOR MAKING ARTICLES FROM POWDERED METALBRIQUEI'S Filed April 5, 1957 United States Patent Joseph B. Brennan,13018 Lake Shore Blvd., Cleveland 8, ghio; I(Ilelen E. Brennan,executrix of said Brennan,

ecease Filed Apr. 5, 1957, Ser. No. 651,063

8 Claims. (Cl. 75-221) The present invention relates generally asindicated to a method of and apparatus for making articles from powderedmetal briquets and more particularly to certain improvements in themethods and processes disclosed in my co-pending applications SerialNos. 104,369, 161,344, and 202,707, all now abandoned. This inventionalso is a continuation-in-part of my co-pending application Serial No.303,317, filed August 8, 1952, now Patent No. 2,803,046, and Ser. No.252,938, filed Oct. 24, 1951, now Patent No. 2,787,817.

It is one object of this invention to provide a method and apparatus bywhich accurate articles of desired denseness (porous or non-porous) maybe formed from powdered metal briquets.

It is another object of this invention to provide a method and apparatusby which and with which a powdered metal briquet may be partially orcompletely fused while contained within a non-distorting heatresistantenclosure, which enclosure may, in some instances, be wholly or partlyof a material which imparts desired physical or chemical properties tothe briquet therein or which bonds to the briquet.

It is another object of this invention to provide a method and apparatusby which and with which a briquet of powdered material, contained in amold, is pre-heated, preferably in vacuum, to render the briquetgas-free and is further heated under vacuum to sinter the briquet whileit is mechanically compacted so as to densify the same and to make itaccurately conform to the mold.

It is another object of this invention to provide a method and apparatusincorporating independent heat control at the briquet pre-heat,degassing and briquet sintering or fusing zones.

It is another object of this invention to provide a method and apparatuswhich involves a two-stage treatment of powdered metal in a mold viz. afirst stage degassing and sintering operation and a second stage furtherdegassing and fusing operation.

Other objects and advantages of my invention will appear as thedescription proceeds.

To the accomplishment of the foregoing and related ends, said inventionthen comprises the features hereinafter fully described and particularlypointed out in the claims, the following description and the annexeddrawings setting forth in detail certain illustrative embodiments of theinvention, these being indicative, however, of but a few of the variousways in which the principles of the invention may be employed.

In said annexed drawings:

Fig. 1 is a cross-section view of a powdered metal briquet andsurrounding enclosure;

2,964,400 Patented Dec. 13, 1960 Fig. 2 is a cross-section view similarto Fig. 1 except that a false piston is included in the enclosure incontact with the powdered metal briquet;

Fig. 3 is a cross-section view showing the false piston of Fig. 2replaced by a piston which is adapted to exert pressure on the powderedmetal briquet when the latter is melted;

Pig. 4 is a cross-section view of a special form of powdered metalbriquet with a surrounding solid metal band to which the powdered metalis to be bonded or alloyed; and i Fig. 5 is a cross-section view of oneform of apparatus which may be employed for the practice of the presentmethod.

Broadly stated, the present method involves the steps of providing apowdered metal briquet, enclosing the briquet in a body ofheat-resistant material, pre-heating the enclosure and briquet thereinin a vacuum chamber to expel and to evacuate substantially all of thegases therefrom, partially or completely fusing the briquet in vacuumprogressively from the bottom to the top thereof, and applyingmechanical pressure on the briquet while in fused condition and exposedto vacuum whereby to form an article of desired density within theenclosure. The enclosure and fused briquet are subsequently cooled tosolidify the metal and then the enclosure may be removed or broken awayfrom the finished article. Similarly, the present apparatus is such asto efficiently perform the foregoing method.

Referring now more particularly to the drawing and first to Fig. 1thereof, the powdered metal briquet 1 is formed in well-known manner bythe mechanical consolidation of the metal powder in suitable diesprovided with cavities of the desired shape and size. The pressurerequired to form the briquet 1 will, of course, vary according to theparticular metal which is used; and, except in the case of low-meltingpoint metals, the pressed compact or briquet is mechanically weak andmust be handled with care. Any of a variety of different metals andalloys may be employed for forming the powdered metal briquet 1.Examples of some of the metals and alloys from which powdered metalbriquets may be formed are: RC B or Ti Alloy A, whose compositions areas follows: Mn 4%, Al. 4%, O 0.2%, N .1% max, and Ti balance; and Fe1.3%, Cr 2.7%, O 25%, N .02% max, C .02% max., and Ti balance.

After the briquet 1 has been formed, it is enclosed in a porous body 2of heat-resistant material, usually a ceramic material including carbon,mica, plaster of Paris, asbestos, stabilized Zirconium oxide, and otherheatresistant and preferably, but not necessarily, non metallicmaterials which can be heated to at least the melting point of thebriquet without melting, burning, or otherwise rendered inoperative bythe melting of the briquet therein. Enclosing of the briquet 1 withinthe body of a heat-resistant material 2 may be done as is disclosed inmy co-pending applications Serial Nos. 161,344 and 202,707.

In the case that the enclosure 2 is in the form of amold made of two ormore pieces, the same may be pre-fired or fused so that said mold willhave a very close fit in the guide portion of the apparatus which willbe presently described.

In Figs. 2 and 3 the briquet 1. is enclosed within a composite enclosurewhich comprises a body 3 of heatresistant material and a plug or piston4 of any desired material such as metal, said piston being positionedadjacent one end of the briquet 1 so as to form therewith and with thebody 3 a cylinder for a piston 5. It can be seen from Fig. 3 that whenthe briquet 1 is fused, pressure on the top of the piston 5 will causethe end of the piston to exert pressure on the top of the fused briquet.The degree of compacting of the melted briquet 1 is determined by thedistance 6 which is additionally selected so that the article will be ofthe desired dimensions in the direction of pressure application thereon.Thus, Where the briquet is of a tubular form as shown in Figs. 1 to 3,the axial dimension thereof will be somewhat greater than that of thefinished article because of the reduction in bulk owing to the fusingthereof and mechanical consolidation in addition, when the piston 5 isemployed as shown in Fig. 3. The diameters of the briquet can, ofcourse, be made to correspond with the desired final diameters of thearticle except to take into account shrinkage owing to thermalcontraction.

In Fig. 4, the powdered metal briquet 7 is formed inside a continuoussolid metal band 8 and the composite briquet 7 and band 3 will beenclosed in heat-resistand material as shown in Fig. 1 or 2 and uponfusing of the briquet 7, the same will become bonded to or alloyed withthe band 8 according to the particular selection of materials for thebriquet and for the band 8.

In Fig. 5, there is shown a preferred form of apparatus through whichthe briquets and surrounding enclosures of Figs. 1 and 3, for example,are adapted to pass. In Fig. 5, the composite enclosures and briquetstherewithin are represented by the reference numeral 10 and for purposesof illustration, these composite enclosures and briquets are of the formillustrated in Fig. 3.

At the top of the apparatus, there is provided a guide tube 11 in whichthe units 10 are superimposed one upon the other with the pistons 5 atthe top of each unit. These units 10 are fed downwardly as by means ofpowerdriven chains or belts 12 which run over sprocket wheels or pulleys14 and 15. The opposed parallel portions of the belts 12 may be pressedinto frictional engagement with the units 10 therebetween as by means ofspring loaded blocks 16. It is to be understood that positive feed meansmay be employed if desired and in such case, the exterior of the units10 may be provided with gear teeth or like formations for meshing withteeth on the wheels 14 or with spaces in the opposed chains 12. One pairof the wheels 14 or 15 will be power-driven and as evident, downwardfeeding of the units 10 may be accomplished at a constant speed.

The units 10 and pistons 5 may be successively pushed down through tube11 by a reciprocating hydraulic ram.

The apparatus below the just-described feeding device comprises a porousor perforate guide tube 17 which may be formed of graphite or likematerial having a nonoxidizable coating on its inner surface. Suchcoating may be of stabilized zirconium oxide or similar refractorymaterial.

The guide tube 17 thus interiorly coated serves to seal the units 10from the surrounding atmosphere and also to provide a precision guide.Said guide tube 17 also alleviates gas contamination, but, at the sametime the porosity of said guide 17 enables evacuation of gases fromwithin the briquets and molds.

The upper portion of the guide tube 17 has a heating chamber 18therearound for pre-heating the units 11 and briquets 1 therein as theypass downwardly through the guide tube 17. Said heating chamber may beheated by the frequency heating element 19.

As the units 10 pass downwardly through the heating chamber 18,substantially all of the gases are expelled and evacuated therefrom.

Below said pre-heating chamber 18 or as shown in the lower portion ofsaid chamber, there is a high frequency heating coil 20 which encirclesthe guide tube 17. Thus, as the units 10 move downwardly at constantspeed, the preheated briquets 1 will be further heated and melted orfused from the bottom thereof upwardly; and, because the gases have beenexpelled by the preheating of said briquet 1 and the enclosure 3therearound and by the vacuum in chamber 18, the melted metal willcompletely conform with the cavities in the enclosures 3 without anytrapped gas pockets. Where the pistons 5 are employed in associationwith the enclosures 3, the resistance to downward movement of the units10 as will be hereinafter explained will cause the end of the piston 5to exert pressure on the fused briquet 1 for densifying the same andfurther causing the melted briquet to completely fill the cavity withinthe enclosure 3 including sharp corners, etc.

The chamber 18 is preferably operated under a vacuum or partial vacuumwith an inert gas such as argon therein when desired by means of avacuum pump and exhaust pipe system attached thereto.

In passing downwardly through the high frequency heating coil 20, thebriquets 1 within the units 10 are successively melted and compacted andthereafter the units 10 pass through a cooling unit 21 which surroundsthe guide tube 17 and through which a suitable cooling medium is adaptedto be circulated. Therefore, as the units 10 pass downwardly through theportion of the guide tube 17 located within the cooling unit 21, theenclosures 3 and melted briquets 1 therewithin are cooled to etfectsolidification of the compacted, sintered briquet 1.

Thus, when the units 10 are discharged from the lower end of the guidetube 17, the finished accurate articles of desired density are removedfrom within the enclosures 3 by breaking away the enclosures 3 where thelatter are of one-piece construction or by opening same for removal ofthe articles therewithin in the case that said enclosures are formed oftwo or more mating pieces.

Where the porous enclosure 3 is formed of graphite or of a ceramicmaterial having carbon therein a certain amount of carbon pick-up may beobtained in this type of fusion casting whereby at least the outer skinof the melted and subsequently solidified briquet 1 is made moreabrasive resistant. For example, in casting titanium alloys, the outsideskin is partially converted to titanium carbide.

In order that a desired resistance may be built up against the downwardmovement of the units 10 through the guide tube 17, there is disposedadjacent the lower end of said guide tube a friction mechanism whichincludes for example, a fixed shoe 22 engaging one side of superimposedunits 10 and a movable spring load shoe 23 which resiliently pressesagainst the opposite side of said units 10. The pressure which the shoe23 exerts against the units 10 may be varied by adjusting thecompression of the spring 24 by means of a suitable adjusting screw 25.Instead of the particular resistance unit shown at the bottom of Fig. 5,other well-known expedients may be employed. For example, a mechanismsuch as used for downward feeding may be positioned adjacent the lowerend of the guide tube 17 and instead of positively driving one pair ofthe wheels 14 or 15, adjustable brakes may be associated therewith forbuilding up the desired resistance against downward movement of theunits 10, or a reciprocating hydraulic ram may be used to assist and/orcontrol the resistance for compression desired.

When the briquet is of the form illustrated in Fig. 4, it is possible tobond the solid metal 8 to the powdered briquet 7 by using the apparatusillustrated in Fig. 5. It should be further noted that the briquets 1may be made of spherical particles of metal or loose spherical particlesmay be loaded into a mold cavity and by fusing the spherical particlesonly partly, the final article will be partially permeable and will beuniformly orificed since in that case, only the contacting portions ofthe spherical particles will bond together.

As one specific example of the present method nickel powder was pressedat a pressure of five tons per square inch to form a briquet that wasenclosed in a porous graphite mold 3 and pushed down through a porousgraphite guide tube 17 having high frequency coils 19 and 20 therearoundoperated at 9600 cycles for preheating the mold and melting the nickelbriquet. The pressure in the vacuum chamber 18 was about 8 to microns ofmercury for degassing the mold and the briquet during heating and fusingof the latter. As the nickel compact was pushed downwardly it was meltedas observed by an optical pyrometer. The pressure used to push thegraphite mold 3 down through the graphite guide tube 17 wasapproximately 100 pounds per square inch and this closed the mold andwhen the cooled mold came out from the lower end of the apparatus thepowdered nickel briquet had been transformed so as to be as dense as asolid rolled bar of nickel within about .02% and equally as dense as acast nickel article. The graphite mold 3 and the guide tube 17 were ofabout 70% density so as to be porous to extract or evacuate gasestherethrough from the nickel briquet prior to fusing and during fusing.

As another example of the present method, a briquet of commercial puretitanium /2" in diameter and 1" in length was degassed in a vacuum offrom 5 to 20 microns of mercury and was heated in the upper zone by thecoil 19 operated at 30 kw. 450,000 cycles to a temperature of about 1800F., again a graphite guide tube 17 and graphite mold 3 having beenemployed. A titanium rod was used as a pusher actuated by a hydrauliccylinder to move the mold 3 and enclosed titanium briquet into thefusion zone which was located about 4" below the upper zone, the lowercoil 20 being operated at 30 kw. and 450,000 cycles for a period of 30seconds which resulted in heating to approximately 2450" F. as read by acomparative radiant pyrometer. At the bottom heating zone, the briquetwas squeezed in the mold 3 with a pressure of 10 tons per square inchapplied through the upper hydraulically actuated rod and while the moldwas supported by a lower hydraulic rod under the same pressure duringthe aforesaid 30 second period.

It has been found that there is a great advantage in preheating thebriquet in a high vacuum to de-gas the same and at this stage thepushing means need not have any appreciable pressure applied thereto.

In the last-mentioned example the pressure in the lower hydrauliccylinder actuated rod was bled by a needle valve so as to inducedownward movement While the pressure was kept at about 10 tons persquare inch. The heat was applied intermittently to the mold andtitanium briquet, and as aforesaid, in the upper zone, the heating maybe conducted at 1250 F. to de-gas and sinter the titanium briquet. Byfollowing this process the final density of the briquet was about 97% ofthat of the published density of the metal titanium. Furthermore, themetal briquets thus formed were practically identical within 5 of a gramand the compression and de-gassing and fusion compressed them to a finalweight within of a gram.

The main feature of this invention is the two-stage operation, that is,vacuum tie-gassing and pro-heating of the briquet so that it is shaperetaining and thereafter further heating the de-gassed briquet anddensifying the metal. The highest temperature needed in pressing andconsolidating titanium powder of 200 mesh at 18 microns Hg vacuum is2880 F., this being just under the reaction temperature of graphite andtitanium. Fusion can also be obtained at 2450 F. at 18 microns Hg vacuumof 200 mesh titanium, without apparent reaction. Sintering may beaccomplished at about 1800 F. on 200 mesh titanium powder and degassingat 18 microns Hg.

Such sintering can be accomplished without compacting pressure, but ittakes about one hour to make a self-sustaining briquet in vacuum.

In any event, in the present method the first stage is a degassing andsintering operation and the second stage is a further degassing andfusing operation.

The present invention may be employed for the making of sinteredelectrodes for electrolytic condensers from titanium tantalum or otherfilm forming metals. By the present method the degree of porosity andhence the area of the electrode exposed to the electrolyte can beregulated.

Other modes of applying the principle of the invention may be employed,change being made as regards the details described, provided thefeatures stated in any of the following claims, or the equivalent ofsuch, be employed.

I therefore particularly point out and distinctly claim as my invention:

1. A method of continuously producing articles from powdered metalcomprising placing such powdered metal in a plurality of enclosures,moving such enclosures seriatim through dual heating zones, preheatingeach enclosure in a first heating zone to degas the powdered metal,heating each enclosure in a second heating zone, releasably opposing themovement of the enclosures through such second zone to force adjacentenclosures together, and then using such force to compress the metalwhile so heated to a desired density to form such articles.

2. A method of continuously producing articles from powdered metalcomprising placing such powdered metal in a plurality of enclosures,moving such enclosures seriatim through dual heating zones, preheatingeach enclosure in a first heating zone to degas and sinter the powderedmetal therein to a shape-retaining form, simultaneously removing thegases expelled from such heating zone, heating each enclosure in asecond heating zone to a temperature higher than the temperature of suchfirst zone, releasably opposing the movement of the enclosures throughsuch second zone to force adjacent enclosures together, using such forcemechanically to compress the metal while so heated to a desired density,and then sequentially cooling each enclosure and compressed metaltherein to form such articles.

3. A method of continuously producing articles from powdered metalcomprising placing such powdered metal in a plurality of enclosures,moving such enclosures successively through a hollow guide member,preheating each enclosure along one zone of such member to degas andsinter the powdered metal to a shape-retaining form, simultaneouslyevacuating the area defined by such one zone to remove the expelledgases and thereby adapt the sintered powdered metal for subsequentcompression, heating each enclosure along a second zone of such memberto a temperature higher than the temperature of such first zone,releasably opposing the movement of such enclosures through the memberto force adjacent enclosures together, and then using such force tocompress the metal while so heated to a desired density.

4. A method of continuously producing articles from powdered metalcomprising placing such powdered metal in a plurality of porous molds,positively driving such molds in superimposed relation successivelythrough a hollow guide member by abutting each mold against a precedingmold, preheating each mold along one zone of such member to degas andsinter the powdered metal to a shape-retaining form, simultaneouslyevacuating the area defined by such one zone to remove the expelledgases from such metal and at least in part through each porous mold andthereby adapt the sintered powdered metal for subsequent compression,heating each mold along a second zone of such member to a temperaturehigher than the temperature of such first zone while simultaneouslyevacuating such second zone also, releasably opposing the movement ofthe molds through the hollow member to force adjacent molds together,using such force to compress the metal in each mold while so heated, andthen cooling the compressed metal before removing each mold from suchhollow member.

5. The method of claim 4 wherein heating each mold along such secondzone includes fusing the metal.

6. The method of claim 4 wherein heating each mold along such secondzone includes further sintering of the metal.

7. The method of claim 5 further including the step of making at leastone of such molds from a carbon-containing ceramic to fuse carbon intothe outer surface of the articles formed as defined.

8 8. The method of claim 4 further including the steps of including ametal band within a mold and bonding such moldable metal thereto.

References Cited in the file of this patent UNITED STATES PATENTS1,648,962 Rentschler et al. Nov. 15, 1927 2,293,400 Morris et al. Aug.18, 1942 2,422,439 Schwarzkopf June 17, 1947 2,480,076 De Marinis Aug.23, 1949 2,803,046 Brennan Aug. 20, 1957 2,818,339 Dodds Dec. 31, 1957

1. A METHOD OF CONTINUOUSLY PRODUCING ARTICLES FROM POWDERED METALCOMPRISING PLACING SUCH POWDERED METAL IN A PLURALITY OF ENCLOSURES,MOVING SUCH ENCLOSURES SERIATIM THROUGH DUAL HEATING ZONES, PREHEATINGEACH ENCLOSURE IN A FIRST HEATING ZONE TO DEGAS THE POWDERED METAL,HEATING SUCH ENCLOSURE IN A SECOND HEATING ZONE, RELEASABLY OPPOSING THEMOVEMENT OF THE ENCLOSURES THROUGH SUCH SECOND ZONE TO FORCE ADJACENTENCLOSURES TOGETHER, AND THEN USING SUCH FORCE TO COMPRESS THE METALWHILE SO HEATED TO A DESIRED DENSITY TO FORM SUCH ARTICLES.